This research proposal is designed to evaluate the renal handling of organic ions in the mammalian kidney. The isolated microperfusion technique permits analysis of the function of the nephron, segment by segment. The proposed experiments will make use of rabbit kidney tubules to investigate: 1) prostaglandin transport characteristics along the nephron; 2) the location and factors that regulate prostaglandin degradation; 3) the effect of prostaglandin on chloride absorption in the thick ascending limb of Henle; 4) collecting tubule synthesis of prostaglandins; 5) tubule factors that may modulate renin release; and 6) cell para-aminohippurate effects on fluid absorption.